Anesthesiology is a complicated business, and it's stressful to keep track of a lot of things at the same time—the right drug cocktail, the correct dosage, coordinating with the rest of medical team, you know, things like that.
And then, there is that risk, teeny or humongous, that something may go wrong—wrong drug cocktail, incorrect dosage, failure to communicate, you know, things like that. It could be stressful for neophytes to keep those "t's" crossed and those "i's" dotted, but consider what might happen if they don’t.
Death, debilitation, paralysis, comas (aka permanent midnight).
But you really don't want to think about these worst-case scenarios. That would really be stressful.